Method for predicting a demand for repair parts

ABSTRACT

A method for predicting a demand for repair parts in which trouble rate in future of the repair parts can be presumed accurately and a reliable demand prediction is possible. The method comprises collecting data of the number of troubles, causes of troubles and the number of years elapsed with respect to a kind of repair parts on the basis of the number of repair parts exchanged owing to troubles within a guarantee period; extracting troubles owing to durability deterioration from the causes of troubles to sum up the number of troubles owing to durability deterioration for each year elapsed; calculating a trouble rate of the repair parts for each year elapsed from the number of troubles summed up for each year elapsed and the number of existing products for each year elapsed; presuming a trouble rate of the repair parts after the guarantee period has elapsed from the calculated trouble rate of the repair parts for each year elapsed; and calculating market scale in future of the repair parts from the presumed trouble rate of the repair parts after the guarantee period has elapsed and a presumed number of the existing products in future to predict a demand for the repair parts.

BACKGROUND OF THE INVENTION

The present invention relates to a method for predicting a demand for repair parts in future.

With respect to a product, the number of existing products in future can be predicted roughly from statistics in the past, and a market scale in the future of repair parts of the product can be obtained roughly by multiplying the number of existing products by a presumed exchange rate of the repair parts. The exchange rate is that for repair and approximately equal to a trouble rate.

However, with respect to a functional part, the trouble rate thereof cannot be obtained theoretically. Therefore, the parts havs been manufactured based on a prediction of market scale that was obtained by experiences or perceptions of experts.

Therefore, accuracy of the predicted trouble rate is very low and the degree of confidence of the predicted demand is poor, so that the number of the repair parts manufactured based on such prediction is not suited to actualities. As the result, stock of the repair parts becomes excessive or short.

The present invention has been made in view of the foregoing, and an object of the invention is to provide a method for predicting a demand for repair parts in which trouble rate in the future of the repair parts can be presumed accurately and a reliable demand prediction is possible.

SUMMARY OF THE INVENTION

In order to achieve the above object, the present invention provides a method for predicting a demand of repair parts comprising: collecting data of the number of troubles, causes of troubles and the number of years elapsed with respect to repair parts on the basis of the repair parts changed owing to troubles within a guarantee period; extracting troubles owing to durability deterioration from the causes of troubles to sum up the number of troubles owing to durability deterioration for each year elapsed; calculating a trouble rate of the repair parts for each year elapsed from the number of troubles summed up for each year elapsed and the number of existing products for each year elapsed; presuming a trouble rate of the repair parts after the guarantee period has elapsed from the calculated trouble rate of the repair parts for each year elapsed; and calculating market scale in the future of the repair parts from the presumed trouble rate of the repair parts after the guarantee period has elapsed and a presumed number of the existing products in the future to predict a demand for the repair parts.

Since about 100% of the parts getting out of order within the guarantee period are exchanged free of charge, a substantially accurate trouble rate can be obtained based on data regarding the repair parts exchanged owing to troubles within the guarantee period.

Among causes of troubles, causes owing to initial quality poorness are those peculiar to an initial period and will not cause trouble after the guarantee period has elapsed. Therefore, if troubles owing to durability deterioration except for the initial quality poorness are extracted as basic data, an accurate trouble rate can be calculated.

If such an accurate trouble rate within the guarantee period is calculated for each year elapsed, a trouble rate after the guarantee period elapsed can be presumed accurately, and a market scale in the future of the repair parts can be calculated from the trouble rate and the presumed number of the products existing in the future to predict a demand for the repair parts accurately.

In the above-mentioned method for predicting a demand for repair parts, the trouble rate of the repair parts after the guarantee period has elapsed may be presumed by making a Weibull-analysis of the trouble rate of the repair parts for each year elapsed.

Since distribution of life times (trouble times) of articles goes roughly along the Weibull distribution, the trouble rate after the guarantee period has elapsed can be presumed accurately by making the Weibull-analysis of the trouble rate of the repair parts for each year elapsed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table showing an example of data of troubles within the guarantee period with respect to repair parts of a motorcar according to an embodiment of the present invention;

FIG. 2 is a table showing troubles of the repair parts for each year elapsed within the guarantee period; and

FIG. 3 shows a Weibull probability sheet on which the trouble rates for each year elapsed of FIG. 2 are plotted to describe a recurrence linear line.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3. According to the embodiment, a demand for repair parts of a motorcar is predicted.

First, data of troubles within the guarantee period are collected with respect to the repair parts.

As shown in FIG. 1, data such as part number, kind of car, trouble occurrence date, days elapsed till trouble occurs, symptoms and guarantee period are collected for each kind of repair parts having got into a trouble.

With respect to the symptoms, if cause of the trouble is durability deterioration, a distinction mark “o” is attached, and if cause of trouble is initial quality poorness, a distinction mark “x” is attached.

From the above-mentioned data, the number of troubles of the repair parts owing to durability deterioration (the distinction mark is “o”) is calculated and listed for each year from the first year of the guarantee period.

FIG. 2 shows an example of the list obtained with regard to a certain kind of repair parts. The guarantee period of the repair parts is 3 years and the cause of trouble is durability deterioration. The list of FIG. 2 also shows the number of existing motorcars using the repair parts for each year.

The number of troubles and the number of existing motorcars for each year elapsed are shown with respect to each year, and a total of the troubles and a total of the existing motorcars for each year elapsed are shown.

Further, trouble rate (%) obtained by dividing the total troubles by the total existing motorcars are shown for each year elapsed.

Such trouble rates for each year elapsed are plotted on a Weibull probability sheet as shown in FIG. 3.

The abscissa (logarithmic scale) of the sheet indicates year elapsed and the ordinate (logarithmic scale) of the sheet indicates trouble rate (%).

The plot P1 shows that the trouble rate at a time when one year elapsed is 0.042%, the plot P2 shows that the trouble rate at a time when two years elapsed is 0.059%, and the plot P3 shows that the trouble rate at a time when three years elapsed is 0.075%.

A recurrence linear line L of the three points (P1, P2, P3) is calculated and described on the Weibull probability sheet as shown in FIG. 3. If the recurrence linear line L is extended beyond the guarantee period, the trouble rate in the future of the repair parts can be presumed. This presumed trouble rate can be regarded as a presumed exchange rate, therefore a demand for a market scale in the future of the repair parts can be obtained substantially exactly by multiplying the number of existing motorcars in the future by the presumed trouble rate.

In FIG. 3, for example, the trouble rate of the repair parts at a time when five years elapsed can be presumed to be about 0.105%. If the presumed number of existing cars of the corresponding year is 71,000, demand of the repair parts at the year can be predicted to be 75 (71,000×0.00105).

Since about 100% of the parts getting out of order within the guarantee period are exchanged free of charge, the trouble rate in the future introduced based on the trouble rate within the guarantee period as mentioned above is substantially exact and reliable.

Since only troubles owing to durability deterioration are extracted as basic data excluding troubles owing to initial quality poorness not influencing future demand, factor to reduce accuracy of trouble rate in the future is eliminated, and a trouble rate of high accuracy can be presumed.

Since distribution of life times (trouble times) of articles goes roughly along the Weibull distribution, the trouble rate after the guarantee period has elapsed can be presumed accurately by making a Weibull-analysis of the trouble rates of the repair parts for each year elapsed.

In the above-mentioned embodiment, demand for repair parts of a motorcar is predicted. But the present invention can be applied to repair parts of any product other than the motorcar, if the existing number of the products can be grasped, and a roughly exact demand can be predicted. 

What is claimed is:
 1. A method for predicting for a demand of repair parts comprising: collecting data of the number of troubles, causes of troubles and the number of years elapsed with respect to a certain kind of repair parts on the basis of said repair parts exchanged owing to troubles within a guarantee period; extracting troubles owing to durability deterioration from said causes of troubles to sum up the number of troubles owing to durability deterioration for each year elapsed; calculating a trouble rate of said repair parts for each year elapsed from said number of troubles summed up for each year elapsed and the number of existing products for each year elapsed; presuming a trouble rate of said repair parts after said guarantee period has elapsed from said calculated trouble rate of said repair parts for each year elapsed; and calculating market scale in future of said repair parts from said presumed trouble rate of said repair parts after said guarantee period has elapsed and a presumed number of said existing products in future to predict a demand for said repair parts.
 2. A method for predicting a demand for repair parts as claimed in claim 1, wherein said trouble rate of said repair parts after said guarantee period has elapsed is presumed by making a Weibull-analysis of said trouble rate of said repair parts for each year elapsed. 